When people leave the theater after a great comedy, conversation spills out of the theater like popcorn onto the floor. Some people recall their favorite scenes while others repeat their favorite lines. There's a cheerful buzz in the air.

At my screening of "Tammy," my audience was severely lacking in the energy department. After the film, there was little chatter to be heard at all. No favorite scenes. No memorable quotes. No buzz.

This isn't unexpected, though, because Melissa McCarthy has essentially played the same character five times over. You know, the vulgar slob who you can't help but love. As long as McCarthy is silly and falls down enough times, the film is sure to be a moneymaker.

As it turns out, McCarthy has reached the end of her rope in "Tammy."

There isn't much of a plot, but here it goes anyway. We follow Tammy as her day goes from bad to worse. First, her car breaks down after she hits a deer on the way to her job at a fast-food restaurant. Then, she loses said job after showing up late and disheveled. Then, once she gets home, she finds her husband Greg (Nate Faxon) making romantic meals for their neighbor (Toni Colette).

This leads her to pack her bags and head out on a road trip to Niagara Falls with her perky alcoholic grandmother Pearl (Susan Sarandon). And being a road-trip film, McCarthy pulls her life together and learns a lesson or two along the way.

Er, scratch that last part.

The biggest problem with "Tammy" is that the two main characters meander from place to place with little rhyme or reason. Their road trip is aimless because the film has little concern with advancing its plot or characters.

Sure, our two leads are heading to Niagara Falls. But "Tammy" gets so sidetracked in the middle that you forget the film began as a road-trip comedy in the first place.

"Tammy" is an uneven series of sketches -- which range from mildly amusing to awkwardly unfunny -- that never really form one cohesive storyline.

Tammy goes jet skiing. Tammy robs Topper Jack's. Tammy attends an all-lesbian 4th of July party. And what's the point of these misadventures? Well, um, she uh, I don’t know.

The screenplay, which McCarthy co-wrote with her husband Ben Falcone (who also directed), is dull and uneven. McCarthy is as energetic as ever, but her screenplay is severely lacking.

As the title character, McCarthy gives a fine, though familiar, performance. She has a few funny one-liners and some of the slapstick entertains, but we've seen her play this character before, and better than she does in "Tammy."

As Tammy's grandmother, Pearl, Susan Sarandon feels slightly out of place. Most of that stems from the fact that Sarandon is only 24 years older than McCarthy.

And for whatever reason, McCarthy and Falcone bring in a multitude of fine actresses, only to do nothing with their characters. The talents of Kathy Bates, Allison Janney, Toni Colette and Sandra Oh are wasted in "Tammy," which is a shame. With that kind of talent on board, their presence in the film is a missed opportunity.

I love McCarthy, and I enjoy the wacky characters she so often plays, but "Tammy" has nothing new to offer. McCarthy is a talented actress and comedienne, but maybe it's time to move on. What else you got?